1. Field of the Invention
The present invention relates to a multimode dielectric resonator apparatus that operates in multiple resonant modes, to a filter and a duplexer that include the resonator and to a communication apparatus that includes the filter and/or the duplexer.
2. Description of the Related Art
Conventionally, a dielectric resonator having a dielectric core arranged in a cavity uses a mode such as a TE01xcex4 mode or a TM01xcex4 mode. In a configuration of a multistage dielectric resonator apparatus formed using a plurality of the aforementioned dielectric resonators, a plurality of the dielectric cores are provided in a cavity.
In the aforementioned configuration using the single resonant mode generated in the single dielectric core, however, the overall size thereof is increased in proportion to the increase in the number of resonators. In addition, the plurality of dielectric cores must be positioned and fixed with high accuracy. This makes it difficult to manufacture dielectric resonator apparatuses, such as dielectric filters, having consistent characteristics.
In view of the above, the present applicant submitted Japanese Unexamined patent application Publication No. 11-145704, regarding a dielectric resonator apparatus in which, while only a single dielectric core is used, the multiplex number is increased. In the proposed dielectric resonator apparatus, at most six modes are generated and can be used. Specifically, with respect to resonant spaces represented by x, y, and z rectangular coordinates, the apparatus generates TMx, TMy, and TMz modes in which electric-field vectors extend toward the x, y, and z axes; and in addition, it generates TEx, TEy, and TEz modes in which electric-field vectors form loops in planes perpendicular to the x, y, and z axes. However, in connection with, for example, positions where coupling grooves are needed, the manufacture of the aforementioned dielectric resonator apparatus involves overcoming significant technical difficulties in order to couple the six individual modes to each other so that all the six modes can be used.
In view of the above, the present invention provides a multimode dielectric resonator apparatus that allows individual resonant modes to be easily obtained, and that allows a large number of resonant-mode sequentially coupled stages to be obtained with a single dielectric core.
The invention also provides a filter using the aforementioned multimode dielectric resonator apparatus.
The invention further provides a duplexer that uses the aforementioned multimode dielectric resonator apparatus.
The invention further provides a communication apparatus using one or more of the above filter and duplexer.
According to one aspect of the present invention, a multimode dielectric resonator apparatus comprises a dielectric core in a conductive cavity. The dielectric core comprises a multi-TM-mode dielectric core portion primarily for determining resonant frequencies of TM modes so that at least one of the TM modes resonates in an operating frequency band, and at least one other TM mode resonates at a frequency higher than the operating frequency band; and a multi-TE-mode dielectric core portion primarily for determining resonant frequencies of TE modes wherein all of the TE modes resonate in the operating frequency band.
More generally, the dielectric core comprises a multi-TM-mode dielectric core portion primarily for determining resonant frequencies of TM modes so that at least one of the TM modes resonates in an operating frequency band, and a multi-TE-mode dielectric core portion primarily for determining resonant frequencies of TE modes wherein at least two of the TE modes resonate in the operating frequency band.
According to the above-described construction, a plurality of TM modes and TE modes can be used, without being influenced by a TM mode which is set to a frequency higher than the operating frequency. Furthermore, a problem can be solved which occurs when one of three TM modes used is unnecessarily coupled to another resonant mode. In addition, predetermined resonant modes can be coupled together in a predetermined condition.
According to another aspect of the invention, in the multimode dielectric resonator apparatus, the TM-mode dielectric core portion is formed in a plate-like shape, the TE-mode dielectric core portion protrudes from a part of the TM-mode dielectric core portion, and the TM-mode dielectric core portion and the TE-mode dielectric core portion are integrated with each other. The TE-mode dielectric core portion may be substantially spherical, quasi-spherical, or ovoid, for example.
According to this construction, the resonant frequency of the TM modes in which the electric-field vectors extend in the thickness direction of the plate-like TM-mode dielectric core portion is arranged to be higher than the resonant frequency of the TM modes in which the electric-field vectors extend in the plane direction thereof, whereby the resonant frequency of the former TM mode is set to a frequency that is higher than the operating frequency band.
With this construction, without being influenced by the shape of the TM-mode dielectric core portion, the TE-mode dielectric core portion having the shape protruding from a part of the TM-mode dielectric core portion can be operated as a multi-TE-mode resonator. The protruding parts may have any shape as long as the five modes of interest (TMx, TMy, TMz, TEx, TEy) have substantially the same resonant frequency. For example, in a quintuple mode filter for the 2 GHz band, the respective resonant frequencies should be within about 0.1 MHZ of each other. In addition, since the TM-mode dielectric core portion and the TE-mode dielectric core portion are integrated with each other, the dielectric core can be easily manufactured, and furthermore, the dielectric core can be easily arranged in the cavity.
According to another aspect of the invention, a filter comprises the aforementioned multimode dielectric resonator apparatus and input/output structures coupled to predetermined resonant modes arranged therein. With this construction, the filter can be formed as a small and low-loss-type filter using multiple resonator stages. The filter thus formed has reduced inter-resonator coupling losses, increased Q values of the individual resonators, and uses the single dielectric core and the single cavity. More specifically, since inter-resonator coupling losses are reduced by using the multiplex resonant modes, and the dielectric core is provided in a central portion of the cavity, electromagnetic fields are concentrated at the dielectric core, conductor losses are reduced, and the Q values of the individual resonators are thereby increased. Therefore, by using the single dielectric core and the single cavity, a small and low-loss-type filter using multiple resonator stages can be provided.
In the filter of the present invention, the aforementioned input/output structures are coupled to TM modes, and further structures are provided for coupling TM modes and TE modes to each other and for coupling TE modes to each other. According to this construction, the input/output structures are securely coupled to electromagnetic fields of TM modes in which, as compared to the TE mode, a larger amount of the electromagnetic field is caused to leak to the outside of the dielectric core, whereby the coupling and the band width can be easily increased. In addition, with sequential coupling of the TE modes, the structure of the coupling structures is simplified, and the design thereof is therefore easy.
According to still another aspect of the present invention, a filter comprises the aforementioned multimode dielectric resonator apparatus, and either coaxial resonators or semicoaxial resonators that are coupled to predetermined modes, and input/output structures coupled to the resonators.
Generally, although secure coupling can be obtained with magnetic-field coupling, it is difficult to provide a coupling loop that couples only to one mode of a multimode dielectric resonator. According to the above-described construction, however, it is the semicoaxial resonators or coaxial resonators that are externally coupled, and secure coupling can thereby be obtained with coupling loops to increase the band width.
In addition, a spurious mode caused by the aforementioned multimode dielectric resonator is minimized by using the semicoaxial resonators or coaxial resonators, and the overall spurious-mode characteristics of the filter can thereby be improved.
Furthermore, since the input/output structures in the multimode dielectric resonator portion are miniaturized, direct passage of signals between the input and the output is reduced. This prevents deterioration in characteristics due to the direct passage of signals from occurring. More specifically, since the semicoaxial resonators or coaxial resonators need not be securely coupled, the input/output structures in the multimode dielectric resonator portion can be small, direct passage of signals between the input and the output is thereby reduced, and deterioration in characteristics due to the direct passage therefore does not occur.
According to still another aspect of the present invention, a duplexer comprises two of the above-described filters. This allows the duplexer to be small overall and to be of a low-loss type. The duplexer can be used as an antenna-sharing unit.
According to still another aspect of the present invention, a communication apparatus comprises at least one of the aforementioned filter and the aforementioned duplexer. The filter may be provided to filter transmission signals or reception signals in a high-frequency circuit. The duplexer may be provided as an antenna-sharing unit. This communication apparatus can be arranged to be small overall and to be of a low-loss type.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings, in which like references denote like elements and parts.